Low melting point silver solder



Feb W5@ w. SOLLER ET AL @949%5@ L Low-MELTING Pomar SILVER SOLDER Filed July 16, 1947 Patented Feb. 7, 1950 Low MELTING roiN'r- SILVER SOLDER Walter Seller and Gerard Krems,` Cincinnati, Ohio, assignors to the United States f America as represented by the Secretary of War Application July 16, 1947, Serial N0. 761,258

(Cl. "15e-e134) Claims.

The invention described herein may be manufactured and used by or for the Government for governmental purposes without payment to us of any royalty thereon.

This invention relates to silver solders of the type especially useful 'for brazing steel; however, they may be used to braze a wide variety of metals.

One object of the invention is to provide a series of Solders of the above character that have a melting point low enough so that some ternpered steels may be brazed with them Without drawing the temper from the steel.

Another object is to provide solders of this character which have an exceptionallyhigh tensile strength so that strong joints may be ob,-

tained. Another object of the invention is tov provide a convenient method for making such solders.

We have discovered that low melting point solders, i. e., having a melting point range between 1100 F. and 1200 F. may be made by mixing a considerable number of the metallic elements which are to be found in columns I B and II-B of the periodic chart of the elements as published in General Chemistry, 5th edition, by H. G. Deming, published by John Wiley & Sons Inc. The term periodic table, as used in the appended claims, refers to Demings table only. These elements are for column I B, copper, silver and gold, which are listed as being ductile. The elements in column II-.B are zinc, cadmium and mercury, which are listed as being low melting.

One characteristic of our solders is that they all contain mercury. Heretofore, mercury has not been regarded as an especially desirable constituent of high strength silver solders for the reason that it was believed to be injurious to strength. We have discovered that high strength solders may be made by the use of at least four of the elements named (two of these being silver and copper) plus mercury and that under these conditions an actual increase of strength results. By the use of the four elements plus mercury, in approximately eutectic mixtures, we are able to provide silver solders which exhibit a homogeneous distribution of solid solutions in copper distributed throughout a solid solution in silver.

.in the illustration, A indicates the solution in copper and B indicates the solution in silver. The accompanying illustration is a photo-micrograph of such structure.

The ranges of Cempsitions. are wmprised in our invention are as follows:

Table A Range 1: Range 2:

Per cent Ber cent Ag 36 49. Ag 36 49 Cu 11 19 ou. 11 1,9 Zn 12 16 Zn 12; .16

Cd -18 3 3 ca 18 33 Hg 0.5 10 0,5.-.10 0.5 3

' rather that certain brazing temperatures are more favorable to increased joint strength tha others. f

Table B CQmP-QSIUOD Brazed Joint 2at Strength,

1g ou Zn od Hg Au FJ P S- 1.

The brazing should be done at a temperature slightly over the melting point, say 50 F. higher.

In making the alloys, we first melt the higher melting metals such as copper and silver together and then introduce the lower melting constituents in the form of amalgams, i. e., those of zinc and cadmium. The melt is then vigorously stirred for a short time at a temperature only slightly above the melting point and then immediately poured out. This method of making the solders is useful where small quantities are to be prepared, but when large quantities are to be manufactured, the melt is held under pressure and the low melting constituents such as mercury, zinc and cadmium, or optionally mercury only or the amalgams may be introduced by pumping the molten substances into the pressure vessel containing the melt. No xed ratios between any two constituents of our mixtures will be necessary. During the addition of mercury in nonpressure melting, a loss of about 25 per cent occurs by evaporation, hence, Table A represents the amounts mixed but does not represent an analysis. Table B, however, represents the approximate composition of the solders before the brazing operation.

Any steel which can be heated to 1150 F. Without losing its temper can be brazed after hardening with our solders. As a specific example of steel, we recommend SAE No. 4340 for this purpose. If the brazing is done in a neutral or reducing atmosphere, no flux will be necessary. Where the brazing is done in air, any flux which melts in the proper range may be employed, for example, a mixture of sodium acid fluoride and sodium meta borate.- Vapor uxes such as boron trifluoride may also be employed. By brazing it about 50 over the melting point of the solder, joint strengths may be obtained which range from 50,000 to 82,000 pounds per square inch. In order to obtain this strength, however, a joint thickness of at least 3/1000 of an inch must be employed since a lower joint-thickness introduces erratic behavior.

The invention claimed is:

1. An alloy suitable for brazing, consisting of Per cent by weight Silver 36 -49 Copper 11 -19 Zinc 12 -16 Cadmium 18 -33 Mercury 1.0-10

said alloy when present to a thickness of at least 0.003 inch in a brazed joint between steel surfaces, being characterized by a tensile strength of 40,000 pounds to 70,000 pounds per square inch and having a melting point range between 1100 F. and 1200 F., and being characterized by suitability for brazing and high strength of the brazed joint.

2. An alloy, suitable for brazing consisting of Per cent by weight Gold 0.5- 3

said alloy, when present to a thickness of at least 0.003 in a brazed joint between steel surfaces, being characterized by a tensile strength of 40,000 pounds to 70,000 pounds per square inch and having a melting point range between 1100 F. and 1200 F.

3. A brazing solder melting between 1100 F. and 1200 F. consisting substantially of Per cent by weight Silver 42.5

Copper 13.6 Zinc 13.6

Cadmium 29.3

Mercury 1.0

4. A brazing solder melting between 1100 F. and 1200o F. consisting substantially of Per cent by weight Silver 37.0

Copper 11.8 Zinc 12.6

Cadmium 27.0

Mercury 9.2 Gold 2.4

5. A brazing solder melting between 1100 F. and 1200 F. consisting substantially of Per cent by weight Silver 38.7 Copper 12.5 Zinc 13.8 Cadmium 27.7 Mercury 5.9 Gold 1.4

WALTER SOLLER. GERARD KRAUS.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 669,425 McAdams Mar. 5, 1901 2,310,231 Goldsmith Feb. 9, 1943 FOREIGN PATENTS Number Country Date 558,873 Great Britain Jan. 25, 1944 

1. AN ALLOY SUITABLE FOR BRAZING, CONSISTING OF 